//! Types that pin data to its location in memory.//!//! It is sometimes useful to have objects that are guaranteed not to move,//! in the sense that their placement in memory does not change, and can thus be relied upon.//! A prime example of such a scenario would be building self-referential structs,//! as moving an object with pointers to itself will invalidate them, which could cause undefined//! behavior.//!//! A [`Pin<P>`] ensures that the pointee of any pointer type `P` has a stable location in memory,//! meaning it cannot be moved elsewhere and its memory cannot be deallocated//! until it gets dropped. We say that the pointee is "pinned".//!//! By default, all types in Rust are movable. Rust allows passing all types by-value,//! and common smart-pointer types such as [`Box<T>`] and `&mut T` allow replacing and//! moving the values they contain: you can move out of a [`Box<T>`], or you can use [`mem::swap`].//! [`Pin<P>`] wraps a pointer type `P`, so [`Pin`]`<`[`Box`]`<T>>` functions much like a regular//! [`Box<T>`]: when a [`Pin`]`<`[`Box`]`<T>>` gets dropped, so do its contents, and the memory gets//! deallocated. Similarly, [`Pin`]`<&mut T>` is a lot like `&mut T`. However, [`Pin<P>`] does//! not let clients actually obtain a [`Box<T>`] or `&mut T` to pinned data, which implies that you//! cannot use operations such as [`mem::swap`]://!//! ```//! use std::pin::Pin;//! fn swap_pins<T>(x: Pin<&mut T>, y: Pin<&mut T>) {//! // `mem::swap` needs `&mut T`, but we cannot get it.//! // We are stuck, we cannot swap the contents of these references.//! // We could use `Pin::get_unchecked_mut`, but that is unsafe for a reason://! // we are not allowed to use it for moving things out of the `Pin`.//! }//! ```//!//! It is worth reiterating that [`Pin<P>`] does *not* change the fact that a Rust compiler//! considers all types movable. [`mem::swap`] remains callable for any `T`. Instead, [`Pin<P>`]//! prevents certain *values* (pointed to by pointers wrapped in [`Pin<P>`]) from being//! moved by making it impossible to call methods that require `&mut T` on them//! (like [`mem::swap`]).//!//! [`Pin<P>`] can be used to wrap any pointer type `P`, and as such it interacts with//! [`Deref`] and [`DerefMut`]. A [`Pin<P>`] where `P: Deref` should be considered//! as a "`P`-style pointer" to a pinned `P::Target` -- so, a [`Pin`]`<`[`Box`]`<T>>` is//! an owned pointer to a pinned `T`, and a [`Pin`]`<`[`Rc`]`<T>>` is a reference-counted//! pointer to a pinned `T`.//! For correctness, [`Pin<P>`] relies on the implementations of [`Deref`] and//! [`DerefMut`] not to move out of their `self` parameter, and only ever to//! return a pointer to pinned data when they are called on a pinned pointer.//!//! # `Unpin`//!//! Many types are always freely movable, even when pinned, because they do not//! rely on having a stable address. This includes all the basic types (like//! [`bool`], [`i32`], and references) as well as types consisting solely of these//! types. Types that do not care about pinning implement the [`Unpin`]//! auto-trait, which cancels the effect of [`Pin<P>`]. For `T: Unpin`,//! [`Pin`]`<`[`Box`]`<T>>` and [`Box<T>`] function identically, as do [`Pin`]`<&mut T>` and//! `&mut T`.//!//! Note that pinning and [`Unpin`] only affect the pointed-to type `P::Target`, not the pointer//! type `P` itself that got wrapped in [`Pin<P>`]. For example, whether or not [`Box<T>`] is//! [`Unpin`] has no effect on the behavior of [`Pin`]`<`[`Box`]`<T>>` (here, `T` is the//! pointed-to type).//!//! # Example: self-referential struct//!//! ```rust//! use std::pin::Pin;//! use std::marker::PhantomPinned;//! use std::ptr::NonNull;//!//! // This is a self-referential struct because the slice field points to the data field.//! // We cannot inform the compiler about that with a normal reference,//! // as this pattern cannot be described with the usual borrowing rules.//! // Instead we use a raw pointer, though one which is known not to be null,//! // as we know it's pointing at the string.//! struct Unmovable {//! data: String,//! slice: NonNull<String>,//! _pin: PhantomPinned,//! }//!//! impl Unmovable {//! // To ensure the data doesn't move when the function returns,//! // we place it in the heap where it will stay for the lifetime of the object,//! // and the only way to access it would be through a pointer to it.//! fn new(data: String) -> Pin<Box<Self>> {//! let res = Unmovable {//! data,//! // we only create the pointer once the data is in place//! // otherwise it will have already moved before we even started//! slice: NonNull::dangling(),//! _pin: PhantomPinned,//! };//! let mut boxed = Box::pin(res);//!//! let slice = NonNull::from(&boxed.data);//! // we know this is safe because modifying a field doesn't move the whole struct//! unsafe {//! let mut_ref: Pin<&mut Self> = Pin::as_mut(&mut boxed);//! Pin::get_unchecked_mut(mut_ref).slice = slice;//! }//! boxed//! }//! }//!//! let unmoved = Unmovable::new("hello".to_string());//! // The pointer should point to the correct location,//! // so long as the struct hasn't moved.//! // Meanwhile, we are free to move the pointer around.//! # #[allow(unused_mut)]//! let mut still_unmoved = unmoved;//! assert_eq!(still_unmoved.slice, NonNull::from(&still_unmoved.data));//!//! // Since our type doesn't implement Unpin, this will fail to compile://! // let mut new_unmoved = Unmovable::new("world".to_string());//! // std::mem::swap(&mut *still_unmoved, &mut *new_unmoved);//! ```//!//! # Example: intrusive doubly-linked list//!//! In an intrusive doubly-linked list, the collection does not actually allocate//! the memory for the elements itself. Allocation is controlled by the clients,//! and elements can live on a stack frame that lives shorter than the collection does.//!//! To make this work, every element has pointers to its predecessor and successor in//! the list. Elements can only be added when they are pinned, because moving the elements//! around would invalidate the pointers. Moreover, the [`Drop`] implementation of a linked//! list element will patch the pointers of its predecessor and successor to remove itself//! from the list.//!//! Crucially, we have to be able to rely on [`drop`] being called. If an element//! could be deallocated or otherwise invalidated without calling [`drop`], the pointers into it//! from its neighbouring elements would become invalid, which would break the data structure.//!//! Therefore, pinning also comes with a [`drop`]-related guarantee.//!//! # `Drop` guarantee//!//! The purpose of pinning is to be able to rely on the placement of some data in memory.//! To make this work, not just moving the data is restricted; deallocating, repurposing, or//! otherwise invalidating the memory used to store the data is restricted, too.//! Concretely, for pinned data you have to maintain the invariant//! that *its memory will not get invalidated or repurposed from the moment it gets pinned until//! when [`drop`] is called*. Memory can be invalidated by deallocation, but also by//! replacing a [`Some(v)`] by [`None`], or calling [`Vec::set_len`] to "kill" some elements//! off of a vector. It can be repurposed by using [`ptr::write`] to overwrite it without//! calling the destructor first.//!//! This is exactly the kind of guarantee that the intrusive linked list from the previous//! section needs to function correctly.//!//! Notice that this guarantee does *not* mean that memory does not leak! It is still//! completely okay not ever to call [`drop`] on a pinned element (e.g., you can still//! call [`mem::forget`] on a [`Pin`]`<`[`Box`]`<T>>`). In the example of the doubly-linked//! list, that element would just stay in the list. However you may not free or reuse the storage//! *without calling [`drop`]*.//!//! # `Drop` implementation//!//! If your type uses pinning (such as the two examples above), you have to be careful//! when implementing [`Drop`]. The [`drop`] function takes `&mut self`, but this//! is called *even if your type was previously pinned*! It is as if the//! compiler automatically called [`Pin::get_unchecked_mut`].//!//! This can never cause a problem in safe code because implementing a type that//! relies on pinning requires unsafe code, but be aware that deciding to make//! use of pinning in your type (for example by implementing some operation on//! [`Pin`]`<&Self>` or [`Pin`]`<&mut Self>`) has consequences for your [`Drop`]//! implementation as well: if an element of your type could have been pinned,//! you must treat [`Drop`] as implicitly taking [`Pin`]`<&mut Self>`.//!//! For example, you could implement `Drop` as follows://!//! ```rust,no_run//! # use std::pin::Pin;//! # struct Type { }//! impl Drop for Type {//! fn drop(&mut self) {//! // `new_unchecked` is okay because we know this value is never used//! // again after being dropped.//! inner_drop(unsafe { Pin::new_unchecked(self)});//! fn inner_drop(this: Pin<&mut Type>) {//! // Actual drop code goes here.//! }//! }//! }//! ```//!//! The function `inner_drop` has the type that [`drop`] *should* have, so this makes sure that//! you do not accidentally use `self`/`this` in a way that is in conflict with pinning.//!//! Moreover, if your type is `#[repr(packed)]`, the compiler will automatically//! move fields around to be able to drop them. It might even do//! that for fields that happen to be sufficiently aligned. As a consequence, you cannot use//! pinning with a `#[repr(packed)]` type.//!//! # Projections and Structural Pinning//!//! When working with pinned structs, the question arises how one can access the//! fields of that struct in a method that takes just [`Pin`]`<&mut Struct>`.//! The usual approach is to write helper methods (so called *projections*)//! that turn [`Pin`]`<&mut Struct>` into a reference to the field, but what//! type should that reference have? Is it [`Pin`]`<&mut Field>` or `&mut Field`?//! The same question arises with the fields of an `enum`, and also when considering//! container/wrapper types such as [`Vec<T>`], [`Box<T>`], or [`RefCell<T>`].//! (This question applies to both mutable and shared references, we just//! use the more common case of mutable references here for illustration.)//!//! It turns out that it is actually up to the author of the data structure//! to decide whether the pinned projection for a particular field turns//! [`Pin`]`<&mut Struct>` into [`Pin`]`<&mut Field>` or `&mut Field`. There are some//! constraints though, and the most important constraint is *consistency*://! every field can be *either* projected to a pinned reference, *or* have//! pinning removed as part of the projection. If both are done for the same field,//! that will likely be unsound!//!//! As the author of a data structure you get to decide for each field whether pinning//! "propagates" to this field or not. Pinning that propagates is also called "structural",//! because it follows the structure of the type.//! In the following subsections, we describe the considerations that have to be made//! for either choice.//!//! ## Pinning *is not* structural for `field`//!//! It may seem counter-intuitive that the field of a pinned struct might not be pinned,//! but that is actually the easiest choice: if a [`Pin`]`<&mut Field>` is never created,//! nothing can go wrong! So, if you decide that some field does not have structural pinning,//! all you have to ensure is that you never create a pinned reference to that field.//!//! Fields without structural pinning may have a projection method that turns//! [`Pin`]`<&mut Struct>` into `&mut Field`://!//! ```rust,no_run//! # use std::pin::Pin;//! # type Field = i32;//! # struct Struct { field: Field }//! impl Struct {//! fn pin_get_field(self: Pin<&mut Self>) -> &mut Field {//! // This is okay because `field` is never considered pinned.//! unsafe { &mut self.get_unchecked_mut().field }//! }//! }//! ```//!//! You may also `impl Unpin for Struct` *even if* the type of `field`//! is not [`Unpin`]. What that type thinks about pinning is not relevant//! when no [`Pin`]`<&mut Field>` is ever created.//!//! ## Pinning *is* structural for `field`//!//! The other option is to decide that pinning is "structural" for `field`,//! meaning that if the struct is pinned then so is the field.//!//! This allows writing a projection that creates a [`Pin`]`<&mut Field>`, thus//! witnessing that the field is pinned://!//! ```rust,no_run//! # use std::pin::Pin;//! # type Field = i32;//! # struct Struct { field: Field }//! impl Struct {//! fn pin_get_field(self: Pin<&mut Self>) -> Pin<&mut Field> {//! // This is okay because `field` is pinned when `self` is.//! unsafe { self.map_unchecked_mut(|s| &mut s.field) }//! }//! }//! ```//!//! However, structural pinning comes with a few extra requirements://!//! 1. The struct must only be [`Unpin`] if all the structural fields are//! [`Unpin`]. This is the default, but [`Unpin`] is a safe trait, so as the author of//! the struct it is your responsibility *not* to add something like//! `impl<T> Unpin for Struct<T>`. (Notice that adding a projection operation//! requires unsafe code, so the fact that [`Unpin`] is a safe trait does not break//! the principle that you only have to worry about any of this if you use `unsafe`.)//! 2. The destructor of the struct must not move structural fields out of its argument. This//! is the exact point that was raised in the [previous section][drop-impl]: `drop` takes//! `&mut self`, but the struct (and hence its fields) might have been pinned before.//! You have to guarantee that you do not move a field inside your [`Drop`] implementation.//! In particular, as explained previously, this means that your struct must *not*//! be `#[repr(packed)]`.//! See that section for how to write [`drop`] in a way that the compiler can help you//! not accidentally break pinning.//! 3. You must make sure that you uphold the [`Drop` guarantee][drop-guarantee]://! once your struct is pinned, the memory that contains the//! content is not overwritten or deallocated without calling the content's destructors.//! This can be tricky, as witnessed by [`VecDeque<T>`]: the destructor of [`VecDeque<T>`]//! can fail to call [`drop`] on all elements if one of the destructors panics. This violates//! the [`Drop`] guarantee, because it can lead to elements being deallocated without//! their destructor being called. ([`VecDeque<T>`] has no pinning projections, so this//! does not cause unsoundness.)//! 4. You must not offer any other operations that could lead to data being moved out of//! the structural fields when your type is pinned. For example, if the struct contains an//! [`Option<T>`] and there is a `take`-like operation with type//! `fn(Pin<&mut Struct<T>>) -> Option<T>`,//! that operation can be used to move a `T` out of a pinned `Struct<T>` -- which means//! pinning cannot be structural for the field holding this data.//!//! For a more complex example of moving data out of a pinned type, imagine if [`RefCell<T>`]//! had a method `fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut T>`.//! Then we could do the following://! ```compile_fail//! fn exploit_ref_cell<T>(rc: Pin<&mut RefCell<T>>) {//! { let p = rc.as_mut().get_pin_mut(); } // Here we get pinned access to the `T`.//! let rc_shr: &RefCell<T> = rc.into_ref().get_ref();//! let b = rc_shr.borrow_mut();//! let content = &mut *b; // And here we have `&mut T` to the same data.//! }//! ```//! This is catastrophic, it means we can first pin the content of the [`RefCell<T>`]//! (using `RefCell::get_pin_mut`) and then move that content using the mutable//! reference we got later.//!//! ## Examples//!//! For a type like [`Vec<T>`], both possibilities (structural pinning or not) make sense.//! A [`Vec<T>`] with structural pinning could have `get_pin`/`get_pin_mut` methods to get//! pinned references to elements. However, it could *not* allow calling//! [`pop`][Vec::pop] on a pinned [`Vec<T>`] because that would move the (structurally pinned)//! contents! Nor could it allow [`push`][Vec::push], which might reallocate and thus also move the//! contents.//!//! A [`Vec<T>`] without structural pinning could `impl<T> Unpin for Vec<T>`, because the contents//! are never pinned and the [`Vec<T>`] itself is fine with being moved as well.//! At that point pinning just has no effect on the vector at all.//!//! In the standard library, pointer types generally do not have structural pinning,//! and thus they do not offer pinning projections. This is why `Box<T>: Unpin` holds for all `T`.//! It makes sense to do this for pointer types, because moving the `Box<T>`//! does not actually move the `T`: the [`Box<T>`] can be freely movable (aka `Unpin`) even if//! the `T` is not. In fact, even [`Pin`]`<`[`Box`]`<T>>` and [`Pin`]`<&mut T>` are always//! [`Unpin`] themselves, for the same reason: their contents (the `T`) are pinned, but the//! pointers themselves can be moved without moving the pinned data. For both [`Box<T>`] and//! [`Pin`]`<`[`Box`]`<T>>`, whether the content is pinned is entirely independent of whether the//! pointer is pinned, meaning pinning is *not* structural.//!//! When implementing a [`Future`] combinator, you will usually need structural pinning//! for the nested futures, as you need to get pinned references to them to call [`poll`].//! But if your combinator contains any other data that does not need to be pinned,//! you can make those fields not structural and hence freely access them with a//! mutable reference even when you just have [`Pin`]`<&mut Self>` (such as in your own//! [`poll`] implementation).//!//! [`Pin<P>`]: struct.Pin.html//! [`Unpin`]: ../marker/trait.Unpin.html//! [`Deref`]: ../ops/trait.Deref.html//! [`DerefMut`]: ../ops/trait.DerefMut.html//! [`mem::swap`]: ../mem/fn.swap.html//! [`mem::forget`]: ../mem/fn.forget.html//! [`Box<T>`]: ../../std/boxed/struct.Box.html//! [`Vec<T>`]: ../../std/vec/struct.Vec.html//! [`Vec::set_len`]: ../../std/vec/struct.Vec.html#method.set_len//! [`Pin`]: struct.Pin.html//! [`Box`]: ../../std/boxed/struct.Box.html//! [Vec::pop]: ../../std/vec/struct.Vec.html#method.pop//! [Vec::push]: ../../std/vec/struct.Vec.html#method.push//! [`Rc`]: ../../std/rc/struct.Rc.html//! [`RefCell<T>`]: ../../std/cell/struct.RefCell.html//! [`Drop`]: ../../std/ops/trait.Drop.html//! [`drop`]: ../../std/ops/trait.Drop.html#tymethod.drop//! [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html//! [`Option<T>`]: ../../std/option/enum.Option.html//! [`VecDeque<T>`]: ../../std/collections/struct.VecDeque.html//! [`RefCell<T>`]: ../cell/struct.RefCell.html//! [`None`]: ../option/enum.Option.html#variant.None//! [`Some(v)`]: ../option/enum.Option.html#variant.Some//! [`ptr::write`]: ../ptr/fn.write.html//! [`Future`]: ../future/trait.Future.html//! [drop-impl]: #drop-implementation//! [drop-guarantee]: #drop-guarantee//! [`poll`]: ../../std/future/trait.Future.html#tymethod.poll//! [`Pin::get_unchecked_mut`]: struct.Pin.html#method.get_unchecked_mut//! [`bool`]: ../../std/primitive.bool.html//! [`i32`]: ../../std/primitive.i32.html#![stable(feature="pin", since="1.33.0")]usecrate::cmp::{self, PartialEq, PartialOrd};
usecrate::fmt;
usecrate::hash::{Hash, Hasher};
usecrate::marker::{Sized, Unpin};
usecrate::ops::{CoerceUnsized, Deref, DerefMut, DispatchFromDyn, Receiver};
/// A pinned pointer.////// This is a wrapper around a kind of pointer which makes that pointer "pin" its/// value in place, preventing the value referenced by that pointer from being moved/// unless it implements [`Unpin`].////// *See the [`pin` module] documentation for an explanation of pinning.*////// [`Unpin`]: ../../std/marker/trait.Unpin.html/// [`pin` module]: ../../std/pin/index.html//// Note: the `Clone` derive below causes unsoundness as it's possible to implement// `Clone` for mutable references.// See <https://internals.rust-lang.org/t/unsoundness-in-pin/11311> for more details.#[stable(feature="pin", since="1.33.0")]#[lang="pin"]#[fundamental]#[repr(transparent)]#[derive(Copy, Clone)]pubstructPin<P> {
pointer: P,
}
// The following implementations aren't derived in order to avoid soundness// issues. `&self.pointer` should not be accessible to untrusted trait// implementations.//// See <https://internals.rust-lang.org/t/unsoundness-in-pin/11311/73> for more details.#[stable(feature="pin_trait_impls", since="1.41.0")]impl<P: Deref, Q: Deref>PartialEq<Pin<Q>>forPin<P>whereP::Target: PartialEq<Q::Target>,
{
fneq(&self, other: &Pin<Q>) ->bool {
P::Target::eq(self, other)
}
fnne(&self, other: &Pin<Q>) ->bool {
P::Target::ne(self, other)
}
}
#[stable(feature="pin_trait_impls", since="1.41.0")]impl<P: Deref<Target: Eq>>EqforPin<P> {}
#[stable(feature="pin_trait_impls", since="1.41.0")]impl<P: Deref, Q: Deref>PartialOrd<Pin<Q>>forPin<P>whereP::Target: PartialOrd<Q::Target>,
{
fnpartial_cmp(&self, other: &Pin<Q>) ->Option<cmp::Ordering> {
P::Target::partial_cmp(self, other)
}
fnlt(&self, other: &Pin<Q>) ->bool {
P::Target::lt(self, other)
}
fnle(&self, other: &Pin<Q>) ->bool {
P::Target::le(self, other)
}
fngt(&self, other: &Pin<Q>) ->bool {
P::Target::gt(self, other)
}
fnge(&self, other: &Pin<Q>) ->bool {
P::Target::ge(self, other)
}
}
#[stable(feature="pin_trait_impls", since="1.41.0")]impl<P: Deref<Target: Ord>>OrdforPin<P> {
fncmp(&self, other: &Self) ->cmp::Ordering {
P::Target::cmp(self, other)
}
}
#[stable(feature="pin_trait_impls", since="1.41.0")]impl<P: Deref<Target: Hash>>HashforPin<P> {
fnhash<H: Hasher>(&self, state: &mutH) {
P::Target::hash(self, state);
}
}
impl<P: Deref<Target: Unpin>>Pin<P> {
/// Construct a new `Pin<P>` around a pointer to some data of a type that/// implements [`Unpin`].////// Unlike `Pin::new_unchecked`, this method is safe because the pointer/// `P` dereferences to an [`Unpin`] type, which cancels the pinning guarantees.////// [`Unpin`]: ../../std/marker/trait.Unpin.html#[stable(feature="pin", since="1.33.0")]#[inline(always)]pubfnnew(pointer: P) ->Pin<P> {
// Safety: the value pointed to is `Unpin`, and so has no requirements// around pinning.unsafe { Pin::new_unchecked(pointer) }
}
/// Unwraps this `Pin<P>` returning the underlying pointer.////// This requires that the data inside this `Pin` is [`Unpin`] so that we/// can ignore the pinning invariants when unwrapping it.////// [`Unpin`]: ../../std/marker/trait.Unpin.html#[stable(feature="pin_into_inner", since="1.39.0")]#[inline(always)]pubfninto_inner(pin: Pin<P>) ->P {
pin.pointer
}
}
impl<P: Deref>Pin<P> {
/// Construct a new `Pin<P>` around a reference to some data of a type that/// may or may not implement `Unpin`.////// If `pointer` dereferences to an `Unpin` type, `Pin::new` should be used/// instead.////// # Safety////// This constructor is unsafe because we cannot guarantee that the data/// pointed to by `pointer` is pinned, meaning that the data will not be moved or/// its storage invalidated until it gets dropped. If the constructed `Pin<P>` does/// not guarantee that the data `P` points to is pinned, that is a violation of/// the API contract and may lead to undefined behavior in later (safe) operations.////// By using this method, you are making a promise about the `P::Deref` and/// `P::DerefMut` implementations, if they exist. Most importantly, they/// must not move out of their `self` arguments: `Pin::as_mut` and `Pin::as_ref`/// will call `DerefMut::deref_mut` and `Deref::deref` *on the pinned pointer*/// and expect these methods to uphold the pinning invariants./// Moreover, by calling this method you promise that the reference `P`/// dereferences to will not be moved out of again; in particular, it/// must not be possible to obtain a `&mut P::Target` and then/// move out of that reference (using, for example [`mem::swap`]).////// For example, calling `Pin::new_unchecked` on an `&'a mut T` is unsafe because/// while you are able to pin it for the given lifetime `'a`, you have no control/// over whether it is kept pinned once `'a` ends:/// ```/// use std::mem;/// use std::pin::Pin;////// fn move_pinned_ref<T>(mut a: T, mut b: T) {/// unsafe {/// let p: Pin<&mut T> = Pin::new_unchecked(&mut a);/// // This should mean the pointee `a` can never move again./// }/// mem::swap(&mut a, &mut b);/// // The address of `a` changed to `b`'s stack slot, so `a` got moved even/// // though we have previously pinned it! We have violated the pinning API contract./// }/// ```/// A value, once pinned, must remain pinned forever (unless its type implements `Unpin`).////// Similarly, calling `Pin::new_unchecked` on an `Rc<T>` is unsafe because there could be/// aliases to the same data that are not subject to the pinning restrictions:/// ```/// use std::rc::Rc;/// use std::pin::Pin;////// fn move_pinned_rc<T>(mut x: Rc<T>) {/// let pinned = unsafe { Pin::new_unchecked(x.clone()) };/// {/// let p: Pin<&T> = pinned.as_ref();/// // This should mean the pointee can never move again./// }/// drop(pinned);/// let content = Rc::get_mut(&mut x).unwrap();/// // Now, if `x` was the only reference, we have a mutable reference to/// // data that we pinned above, which we could use to move it as we have/// // seen in the previous example. We have violated the pinning API contract./// }/// ```////// [`mem::swap`]: ../../std/mem/fn.swap.html#[stable(feature="pin", since="1.33.0")]#[inline(always)]pubunsafefnnew_unchecked(pointer: P) ->Pin<P> {
Pin { pointer }
}
/// Gets a pinned shared reference from this pinned pointer.////// This is a generic method to go from `&Pin<Pointer<T>>` to `Pin<&T>`./// It is safe because, as part of the contract of `Pin::new_unchecked`,/// the pointee cannot move after `Pin<Pointer<T>>` got created./// "Malicious" implementations of `Pointer::Deref` are likewise/// ruled out by the contract of `Pin::new_unchecked`.#[stable(feature="pin", since="1.33.0")]#[inline(always)]pubfnas_ref(&self) ->Pin<&P::Target> {
// SAFETY: see documentation on this functionunsafe { Pin::new_unchecked(&*self.pointer) }
}
/// Unwraps this `Pin<P>` returning the underlying pointer.////// # Safety////// This function is unsafe. You must guarantee that you will continue to/// treat the pointer `P` as pinned after you call this function, so that/// the invariants on the `Pin` type can be upheld. If the code using the/// resulting `P` does not continue to maintain the pinning invariants that/// is a violation of the API contract and may lead to undefined behavior in/// later (safe) operations.////// If the underlying data is [`Unpin`], [`Pin::into_inner`] should be used/// instead.////// [`Unpin`]: ../../std/marker/trait.Unpin.html/// [`Pin::into_inner`]: #method.into_inner#[stable(feature="pin_into_inner", since="1.39.0")]#[inline(always)]pubunsafefninto_inner_unchecked(pin: Pin<P>) ->P {
pin.pointer
}
}
impl<P: DerefMut>Pin<P> {
/// Gets a pinned mutable reference from this pinned pointer.////// This is a generic method to go from `&mut Pin<Pointer<T>>` to `Pin<&mut T>`./// It is safe because, as part of the contract of `Pin::new_unchecked`,/// the pointee cannot move after `Pin<Pointer<T>>` got created./// "Malicious" implementations of `Pointer::DerefMut` are likewise/// ruled out by the contract of `Pin::new_unchecked`.////// This method is useful when doing multiple calls to functions that consume the pinned type.////// # Example////// ```/// use std::pin::Pin;////// # struct Type {}/// impl Type {/// fn method(self: Pin<&mut Self>) {/// // do something/// }////// fn call_method_twice(mut self: Pin<&mut Self>) {/// // `method` consumes `self`, so reborrow the `Pin<&mut Self>` via `as_mut`./// self.as_mut().method();/// self.as_mut().method();/// }/// }/// ```#[stable(feature="pin", since="1.33.0")]#[inline(always)]pubfnas_mut(&mutself) ->Pin<&mutP::Target> {
// SAFETY: see documentation on this functionunsafe { Pin::new_unchecked(&mut*self.pointer) }
}
/// Assigns a new value to the memory behind the pinned reference.////// This overwrites pinned data, but that is okay: its destructor gets/// run before being overwritten, so no pinning guarantee is violated.#[stable(feature="pin", since="1.33.0")]#[inline(always)]pubfnset(&mutself, value: P::Target)
whereP::Target: Sized,
{
*(self.pointer) =value;
}
}
impl<'a, T: ?Sized>Pin<&'aT> {
/// Constructs a new pin by mapping the interior value.////// For example, if you wanted to get a `Pin` of a field of something,/// you could use this to get access to that field in one line of code./// However, there are several gotchas with these "pinning projections";/// see the [`pin` module] documentation for further details on that topic.////// # Safety////// This function is unsafe. You must guarantee that the data you return/// will not move so long as the argument value does not move (for example,/// because it is one of the fields of that value), and also that you do/// not move out of the argument you receive to the interior function.////// [`pin` module]: ../../std/pin/index.html#projections-and-structural-pinning#[stable(feature="pin", since="1.33.0")]pubunsafefnmap_unchecked<U, F>(self, func: F) ->Pin<&'aU>whereU: ?Sized,
F: FnOnce(&T) ->&U,
{
letpointer=&*self.pointer;
letnew_pointer=func(pointer);
Pin::new_unchecked(new_pointer)
}
/// Gets a shared reference out of a pin.////// This is safe because it is not possible to move out of a shared reference./// It may seem like there is an issue here with interior mutability: in fact,/// it *is* possible to move a `T` out of a `&RefCell<T>`. However, this is/// not a problem as long as there does not also exist a `Pin<&T>` pointing/// to the same data, and `RefCell<T>` does not let you create a pinned reference/// to its contents. See the discussion on ["pinning projections"] for further/// details.////// Note: `Pin` also implements `Deref` to the target, which can be used/// to access the inner value. However, `Deref` only provides a reference/// that lives for as long as the borrow of the `Pin`, not the lifetime of/// the `Pin` itself. This method allows turning the `Pin` into a reference/// with the same lifetime as the original `Pin`.////// ["pinning projections"]: ../../std/pin/index.html#projections-and-structural-pinning#[stable(feature="pin", since="1.33.0")]#[inline(always)]pubfnget_ref(self) ->&'aT {
self.pointer
}
}
impl<'a, T: ?Sized>Pin<&'amutT> {
/// Converts this `Pin<&mut T>` into a `Pin<&T>` with the same lifetime.#[stable(feature="pin", since="1.33.0")]#[inline(always)]pubfninto_ref(self) ->Pin<&'aT> {
Pin { pointer: self.pointer }
}
/// Gets a mutable reference to the data inside of this `Pin`.////// This requires that the data inside this `Pin` is `Unpin`.////// Note: `Pin` also implements `DerefMut` to the data, which can be used/// to access the inner value. However, `DerefMut` only provides a reference/// that lives for as long as the borrow of the `Pin`, not the lifetime of/// the `Pin` itself. This method allows turning the `Pin` into a reference/// with the same lifetime as the original `Pin`.#[stable(feature="pin", since="1.33.0")]#[inline(always)]pubfnget_mut(self) ->&'amutTwhereT: Unpin,
{
self.pointer
}
/// Gets a mutable reference to the data inside of this `Pin`.////// # Safety////// This function is unsafe. You must guarantee that you will never move/// the data out of the mutable reference you receive when you call this/// function, so that the invariants on the `Pin` type can be upheld.////// If the underlying data is `Unpin`, `Pin::get_mut` should be used/// instead.#[stable(feature="pin", since="1.33.0")]#[inline(always)]pubunsafefnget_unchecked_mut(self) ->&'amutT {
self.pointer
}
/// Construct a new pin by mapping the interior value.////// For example, if you wanted to get a `Pin` of a field of something,/// you could use this to get access to that field in one line of code./// However, there are several gotchas with these "pinning projections";/// see the [`pin` module] documentation for further details on that topic.////// # Safety////// This function is unsafe. You must guarantee that the data you return/// will not move so long as the argument value does not move (for example,/// because it is one of the fields of that value), and also that you do/// not move out of the argument you receive to the interior function.////// [`pin` module]: ../../std/pin/index.html#projections-and-structural-pinning#[stable(feature="pin", since="1.33.0")]pubunsafefnmap_unchecked_mut<U, F>(self, func: F) ->Pin<&'amutU>whereU: ?Sized,
F: FnOnce(&mutT) ->&mutU,
{
letpointer=Pin::get_unchecked_mut(self);
letnew_pointer=func(pointer);
Pin::new_unchecked(new_pointer)
}
}
#[stable(feature="pin", since="1.33.0")]impl<P: Deref>DerefforPin<P> {
typeTarget=P::Target;
fnderef(&self) ->&P::Target {
Pin::get_ref(Pin::as_ref(self))
}
}
#[stable(feature="pin", since="1.33.0")]impl<P: DerefMut<Target: Unpin>>DerefMutforPin<P> {
fnderef_mut(&mutself) ->&mutP::Target {
Pin::get_mut(Pin::as_mut(self))
}
}
#[unstable(feature="receiver_trait", issue="none")]impl<P: Receiver>ReceiverforPin<P> {}
#[stable(feature="pin", since="1.33.0")]impl<P: fmt::Debug>fmt::DebugforPin<P> {
fnfmt(&self, f: &mutfmt::Formatter<'_>) ->fmt::Result {
fmt::Debug::fmt(&self.pointer, f)
}
}
#[stable(feature="pin", since="1.33.0")]impl<P: fmt::Display>fmt::DisplayforPin<P> {
fnfmt(&self, f: &mutfmt::Formatter<'_>) ->fmt::Result {
fmt::Display::fmt(&self.pointer, f)
}
}
#[stable(feature="pin", since="1.33.0")]impl<P: fmt::Pointer>fmt::PointerforPin<P> {
fnfmt(&self, f: &mutfmt::Formatter<'_>) ->fmt::Result {
fmt::Pointer::fmt(&self.pointer, f)
}
}
// Note: this means that any impl of `CoerceUnsized` that allows coercing from// a type that impls `Deref<Target=impl !Unpin>` to a type that impls// `Deref<Target=Unpin>` is unsound. Any such impl would probably be unsound// for other reasons, though, so we just need to take care not to allow such// impls to land in std.#[stable(feature="pin", since="1.33.0")]impl<P, U>CoerceUnsized<Pin<U>>forPin<P>whereP: CoerceUnsized<U> {}
#[stable(feature="pin", since="1.33.0")]impl<P, U>DispatchFromDyn<Pin<U>>forPin<P>whereP: DispatchFromDyn<U> {}